Method for manufacturing a stamper

ABSTRACT

A method for manufacturing an imprint stamper includes the steps of forming a first electroformed layer on a concavo-convex pattern of an original disk with the pattern, peeling off the first electroformed layer to provide a first stamper, forming a second electroformed layer on a concavo-convex pattern of the first stamper, peeling off the second electroformed layer to provide a second stamper, forming a third electroformed layer on a concavo-convex pattern of the second stamper, and peeling off the third electroformed layer to provide a third stamper. In addition, a conductive film is formed at least on one of a bottom of the concave portion and a top surface of the convex portion of the concavo-convex pattern at least in one of the first stamper and the second stamper.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-245967, filed on Sep. 25, 2008, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a stamper as a metal mold used for a technique for manufacturing recording media, the technique being injection molding or imprinting for transferring a recording pattern onto a large amount of recording media.

DESCRIPTION OF THE BACKGROUND

A recent increase in recording capacity for information recording apparatuses is due to the improvement of the recording density of recording media. There is known, e.g., a discrete track recording (DTR) magnetic medium as such a recording medium, the DTR medium being provided with two or more data-recording tracks concentrically formed thereon, the tracks forming a pattern composed of magnetic and nonmagnetic portions.

Methods for manufacturing such a magnetic recording medium include a nanoimprint method, the method employing a nickel (Ni) stamper as a metal mold. JP-A 2008-12705 (KOKAI) discloses the nanoimprint method.

Actually, a stamper for manufacturing DTR magnetic recording media has a concavo-convex pattern with a track pitch of 100 nm or less, thus requiring a microfabrication technique capable of forming the pattern.

However, as the track pitch of the concavo-convex pattern thus becomes narrow for high-density recording, a thinner resist layer is more advantageous for an EB drawing. That is, a performance of the EB drawing is enhanced when employing a thinner resist layer. This rate controlling of the EB drawing results in the thinner resist layer, reducing a difference in height between concave and convex portions on an original disk thus manufactured. According to a stamper with a thin concavo-convex pattern, manufactured using the above-mentioned original disk, an insufficient transfer often takes place while imprinting, giving rise to a defective concavo-convex pattern of the medium manufactured using the stamper. Moreover, a reduced difference in height between concave and convex portions on the medium imprinted reduces a degree of separation between magnetic signals on adjacent tracks of the recording medium, causing difficulty in high-density recording.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a method for manufacturing a stamper includes the steps of forming a first electroformed layer on a concavo-convex pattern of an original disk with the pattern, peeling off the first electroformed layer to provide a first stamper, forming a second electroformed layer on a concavo-convex pattern of the first stamper, peeling off the second electroformed layer to provide a second stamper, forming a third electroformed layer on a concavo-convex pattern of the second stamper, and peeling off the third electroformed layer to provide a third stamper. In addition, a conductive film is formed at least on one of a bottom of a concave portion and a top surface of a convex portion of the concavo-convex pattern at least in one of the first stamper and the second stamper.

According to a second aspect of the invention, a method for manufacturing a stamper includes the following 3 steps. A first step includes forming a conductive film on a concavo-convex pattern of an original disk with the pattern, forming an electroformed layer on the conductive film, and peeling off the conductive film and the electroformed layer from the original disk to provide a father stamper. A second step includes forming a releasing layer on a concavo-convex pattern of the father stamper, forming an electroformed layer on the releasing layer, and subsequently peeling off the electroformed layer from the father stamper to provide a mother stamper. A third step includes forming a conductive film at least on one of a bottom surface of a concave portion and a top surface of a convex portion of the concavo-convex pattern at least in the mother stamper, forming a releasing layer on the conductive film, which is followed by forming an electroformed layer on the releasing layer, and subsequently peeling off the electroformed layer to provide a son stamper.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.

FIGS. 1A to 1H are sectional views schematically showing steps of manufacturing a stamper according to an embodiment of the present invention.

FIGS. 2A to 2D are sectional views schematically showing steps of manufacturing a stamper according to the embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

An embodiment of the present invention is explained below with reference to drawings.

Embodiment

FIGS. 1A to 1H are sectional views schematically showing steps for manufacturing a stamper according to an embodiment of the invention. The stamper is manufactured as will be described below, using a coating applicator, a drawing apparatus, a development apparatus, a deposition system and an electroforming apparatus.

As shown in FIG. 1A, a glass substrate or a Si substrate is coated with a photoresistive resin (referred to as a “resist”) by spin coating using a coating applicator, thus forming a resist layer 12.

Next, as shown in FIG. 1B, a latent image is formed by irradiating the resist layer 12 with an electron beam (EB) using an EB drawing apparatus. Furthermore, the resist layer 12 with the latent image thereon is developed to form a concavo-convex pattern using a development apparatus. A substrate thus manufactured through a series of these steps is called an original disk 10.

Next, as shown in FIG. 1C, a conducting film 13 is formed on the concavo-convex pattern of the original disk 10, and an electroformed layer 14 is further formed on the conducting film 13 using an electroforming apparatus. Then, a double layer formed of the conducting film 13 and the electroformed layer 14 is peeled off from the original disk 10 to provide a father stamper 15 as a first stamper shown in FIG. 1E.

Next, as shown in FIG. 1F, an oxide film 16 is formed as a releasing layer on a concavo-convex pattern of the father stamper 15 by anodic oxidation coating or oxygen plasma ashing. Then, as shown in FIG. 1G, an electroformed layer 17 is formed on the oxide film 16, the oxide film 16 and electroformed layer 17 being peeled off from the father stamper 15 to provide a mother stamper 18 as a second stamper.

According to the invention, the mother stamper 18 is subjected to a treatment. The treatment allows it to enhance the difference in height between the concave and convex portions thereof, i.e., the difference in height between bottoms of the concave portions and top surfaces of the convex portions. As shown in FIG. 2A, the treatment provides a conductive film 19 to the bottoms of the concave portions and the top surfaces of the convex portions of the mother stamper 18. The conductive film 19 is formed on the concavo-convex pattern of the mother stamper 18. Specifically, the mother stamper 18 has a concavo-convex pitch, i.e., a predetermined track pitch L_(t)=100 nm and a sidewall slope of the concavo-convex pattern D_(t)=90°, as shown in FIG. 2A. The conductive film 19 was deposited by DC sputtering under a sputtering pressure of 1.0 Pa, at a discharge power of 100 W and for a deposition time of 225 sec. The sputtering under these conditions provided a 10-nm thick film and a 20-nm thick film to bottoms 18 a of the concave portions and top surfaces 18 b of the convex portions, respectively, thus enabling to make the conductive film on the top surfaces thicker than that on the bottoms. As a result, it was achieved that the difference in height between the concave and convex portions was enhanced by 10 nm, compared with that before the treatment.

In the treatment, the conductive film 19 may be deposited on sidewalls of the concavo-convex portions. Furthermore, it is preferable that the mother stamper 18 is subjected to the treatment just after peeling off the mother stamper 18 from the father stamper 15. This is because a surface of the mother stamper 18 oxidizes progressively with time, obstructing a stable formation of the conductive film 19 on the surface.

Next, a releasing layer 20 is formed on the surface of the conductive layer 19 by oxygen RIE (Reactive Ion Etching), etc., as shown in FIG. 2B. The mother stamper with the releasing layer 20 thereon is immersed in a nickel-sulfamate bath to electroform an electroformed layer 21. After that, the electroformed layer 21 is peeled off from the mother stamper to duplicate a son stamper 22 as a third stamper shown in FIG. 2D. In addition, a concavo-convex-patterned surface of the son stamper 22 is spin coated with a protective film, and then dried. The son stamper 22 is subjected to a rear surface grind as needed and punching to obtain a final stamper for transferring a final recording pattern onto massive amounts of magnetic recording media.

Here, a material consisting primarily of Ni is employed for the conductive film 19 and the releasing layer, as Ni has a high mechanical strength, resistance to corrosion and wear, and high adhesion to the electroformed Ni. In addition, Ni or a Ni-based metal containing Co, S, B, or P is employed for the electroformed layer 21.

In a specific example shown in FIG. 2A, the track pitch L_(t) and the slope D_(t) of the track sidewall of the concavo-convex pattern of the mother stamper 18 was set to 100 nm and 90°, respectively. However, these numerals are specified just as one example. That is, the track pitch L_(t) may range from 10 to 100 nm, and the slope of the track sidewall D_(t) may range from 60 to 100°. Here, the reason for setting the lowest track pitch to 10 nm is that even forming the conductive film 19 on the surface of the mother stamper 18 may not allow it to easily give a difference in height between the concave and convex portions when the track pitch is under 10 nm. Here, the reason for setting the slope D_(t) of track sidewall to a range from 60 to 100° is that it becomes impossible to acquire a sufficient area for the magnetic portion of the medium when D_(t) is under 60°, whereas it becomes difficult to peel off the releasing layer 20 from the mother stamper 18 when D_(t) is larger than 100°. As mentioned above, the thicknesses of the conductive film formed on the mother stamper 18 are set to 10 nm and 20 nm at the bottom and the top surface, respectively. Meanwhile, these thicknesses are specified just as an example. It is possible to make the conductive film on the top surface thicker than that on the bottoms by selecting sputtering conditions such as a sputtering pressure, a discharge power, a sputtering time, etc.

As described above, the mother stamper 18 was obtained such that the conductive film was provided to the bottoms and top surfaces of the concavo-convex pattern to enhance the difference in height between the convex and concave portions. The son stamper 22 duplicated using such a mother stamper 18 is also made to have an enhanced difference in height between the convex and concave portions. Hence, the son stamper 22 allows it to eliminate insufficient transfers of the pattern while subsequent imprinting and to surely form the concavo-convex pattern of the resist mask on the medium. A difference in height between the convex and concave portions of the imprinted medium itself may also be enhanced to heighten a degree of separation between magnetic signals on adjacent tracks of the recording medium. Such a medium enables higher recording density. The mother stamper 18 has its surface of the concavo-convex pattern coated with the conductive layer, standing long use without wear, even if the mother stamper 18 is used repeatedly for duplicating the son stamper 18.

The present invention is not limited to the above-described embodiment, but may be variously modified for the practice of the invention unless the scope of the invention is altered. For example, it was described above that the mother stamper 18 was subjected to the treatment, so that the difference in height between the concave and convex portions of the concavo-convex pattern was enhanced. As a modified embodiment, the mother stamper 18 and the father stamper 15 may be subjected to the treatments for enhancing the differences in height between the concave and convex portions of the respective concavo-convex patterns. In this case, it is important that the respective treatments provide the conductive film to the bottoms of the concave portions and the top surfaces of the convex portions of the respective concavo-convex patterns. It was described throughout that the conductive film was formed on the bottoms of the concave portions and the top surfaces of the convex portions of the concavo-convex pattern. However, what is important is to form the conductive film at least on the top surfaces of the convex portions of the concavo-convex pattern. Moreover, although the above-described shapes or numerals of the embodiment are different partially from those of the practical examples, the shapes or numerals may be altered with reference to publicly known techniques.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiment shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the inventive concept as defined by the claims and their equivalents. 

1. A method for manufacturing a stamper, comprising the steps of: forming a first electroformed layer on a concavo-convex pattern of an original disk; peeling off the first electroformed layer to provide a first stamper; forming a second electroformed layer on a concavo-convex pattern of the first stamper; peeling off the second electroformed layer to provide a second stamper; forming a third electroformed layer on a concavo-convex pattern of the second stamper; and peeling off the third electroformed layer to provide a third stamper, wherein a conductive film is formed on at least one of a bottom of a concave portion and a top surface of a convex portion of the concavo-convex pattern in at least one of the first stamper and the second stamper.
 2. The method according to claim 1, wherein the conductive film is formed so as to make the conductive film on the top surface of the convex portion thicker than that on the bottom surface of the concave portion.
 3. The method according to claim 1, wherein the conductive film is formed on the concavo-convex pattern by a sputtering method.
 4. The method according to claim 1, wherein the conductive film is formed on a stamper having the concavo-convex pattern with a track pitch ranging from 10 nm to 100 nm and a sidewall slope ranging from 60° to 100°.
 5. The method according to claim 1, wherein the conductive film includes nickel.
 6. The method according to claim 2, wherein the conductive film includes nickel.
 7. The method according to claim 3, wherein the conductive film includes nickel.
 8. The method according to claim 4, wherein the conductive film includes nickel.
 9. A method for manufacturing a stamper comprising the steps of: a first step comprising: forming a conductive film on a concavo-convex pattern of an original disk; forming an electroformed layer on the conductive film; and peeling off the conductive film and the electroformed layer from the original disk so as to provide a father stamper; a second step comprising: forming a releasing layer on a concavo-convex pattern of the father stamper; forming an electroformed layer on the releasing layer; and peeling off the electroformed layer from the father stamper so as to provide a mother stamper; and a third step comprising: forming a conductive film on at least one of a bottom surface of a concave portion and a top surface of a convex portion of the concavo-convex pattern in at least the mother stamper; forming a releasing layer on the conductive film, which is followed by forming a electroformed layer thereon; and peeling off the electroformed layer so as to provide a son stamper. 